Density functional theory (DFT) calculations are performed with the Vienna ab initio simulation package (VASP) which adopts the projector-augmented wave method [1]}. The plane-wave energy cutoff is set at 400 eV. The exchange-correlation functional of the Perdew-Burke-Ernzerhof (PBE) type[2]}, [3]}, [4]} is used for both structural relaxations and self-consistent electronic calculations. The convergence criteria for the electronic iteration and geometry optimization are set to 10\(^{-6}\)  eV and 0.001 eV/Å, respectively. The BZ is sampled by a 9\(\times \) 9\(\times \) 7 k-mesh for the normal phase and a 6\(\times \) 6\(\times \) 4 k-mesh for the CDW phase within the Gamma-centered scheme. Phonon spectrum is calculated with PHONOPY code [5]}, using density-functional perturbation theory (DFPT) method. Joint DOS is calculated based on Wannier orbitals which are obtained through VASP2WANNIER90 interface [6]}, 60 orbitals are included with SOC being considered.
